1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
In this specification, a semiconductor device means all types of devices which can function by utilizing semiconductor characteristics, and a display device, an electro-optical device, a photoelectric conversion device, a semiconductor circuit, and an electronic appliance are all semiconductor devices.
2. Description of the Related Art
As one type of field-effect transistor, a thin film transistor whose channel region is formed using a semiconductor film that is formed over a substrate having an insulating surface is known. Techniques in which an amorphous silicon film, a microcrystalline silicon film, or a polycrystalline silicon film is used for a semiconductor film used for a channel region of a thin film transistor have been disclosed (see Patent Documents 1 to 5). A typical application of thin film transistors is a liquid crystal television device, in which thin film transistors are put to practical use as a switching transistor for each pixel that constitutes a display screen.